1. Field of the Present Invention
The present invention relates generally to a wireless communication device and a channel estimation/separation method in a wireless LAN, mobile communications, digital broadcasting, etc that utilize MIMO (Multiple Input Multiple Output)-OFDM (Orthogonal Frequency Division Multiplexing), and more particularly to a wireless communication device and a channel estimation/separation method that are capable of estimating and separating a transfer function of a channel with high accuracy.
2. Description of the Related Art
The MIMO (Multiple Input Multiple Output) system, which is a generic term of multiple-input multiple-output systems, represents a system of transmitting information by use of array antennas for both of transmission and reception in communication fields. The MIMO system is utilized in wireless LANs and in mobile communications at the present and is expected to be applied to broadband wireless communications in the future.
A study of a MIMO-OFDM wireless communication system utilizing the Orthogonal Frequency Division Multiplexing (OFDM), which is a tough scheme against frequency selective fading and has high frequency availability efficiency, shows a progress for handling broadband information signals by the MIMO.
In the MIMO-OFDM wireless communication system, it is required that a channel transfer function be estimated for estimating fluctuations in amplitude and in phase on a subcarrier-by-subcarrier basis, which occur on transmission paths. The channel estimation in the MIMO-OFDM requires measuring a deviation from an idealistic state of the amplitude and the phase on the subcarrier-by-subcarrier basis of a frequency of a pilot symbol of each antenna by using the transmitted pilot symbol (training symbol) and the received signal. If disabled to perform the high-accuracy channel estimation, it is impossible to demodulate reliable data by the MIMO-OFDM system.
Some channel estimation methods are known as the conventional arts. Non-Patent document 1 (Y. Li “Simplified channel estimation for OFDM systems with multiple transmit antennas” (IEEE Trans. Wireless Commun., vol. 1, pp. 67-75, January. 2002)) discloses a technology that needs a large quantity of multiplication and a large amount of IFFT beforehand, resulting in a tremendous quantity of arithmetic operations. Further, Non-Patent document 2 (G. Auer “Channel Estimation for OFDM with Cyclic Delay Diversity” (Proc. IEEE PIMRC 2004, Vol. 3, pp. 1792-1796, Sep. 2004)) discloses a technology capable of improving accuracy of the channel estimation and simultaneously performing the channel separation by using a Wiener filter in a time domain that obtains a minimum mean square error (MMSE). The MMSE filter (Wiener filter) requires a priori statistic characteristic of the channel, however, this characteristic can be obtained also by estimation. Generally, however, the receiving side does not recognize the known statistic characteristic of the channel. The estimation of the statistic characteristic of the channel, which needs calculation of correlation etc, is intricate of the arithmetic operation and is large of the arithmetic quantity. Further, a problem about the estimation accuracy arises if noises and interference are large. It is to be noted that the other conventional arts related to the invention of the present application are disclosed in the Japanese Patent Application Laid-Open Publication No. 2004-180313.